Analogy and similarity are often assumed to be distinct psychological processes. In contrast to this position, the authors suggest that both similarity and analogy involve a process of structural alignment and mapping, that is, that similarity is like analogy. In this article, the authors first describe the structure-mapping process as it has been worked out for analogy. Then, this view is extended to similarity, where it is used to generate new predictions. Finally, the authors explore broader implications of structural alignment for psychological processing.

This paper presents a learning theory pertinent to dynamic decision making (DDM) called instancebased learning theory (IBLT). IBLT proposes five learning mechanisms in the context of a decision-making process: instance-based knowledge, recognition-based retrieval, adaptive strategies, necessity-based choice, and feedback updates. IBLT suggests in DDM people learn with the accumulation and refinement of instances, containing the decision-making situation, action, and utility of decisions. As decision makers interact with a dynamic task, they recognize a situation according to its similarity to past instances, adapt their judgment strategies from heuristic-based to instance-based, and refine the accumulated knowledge according to feedback on the result of their actions. The IBLT’s learning mechanisms have been implemented in an ACT-R cognitive model. Through a series of experiments, this paper shows how the IBLT’s learning mechanisms closely approximate the relative trend magnitude and performance of human data. Although the cognitive model is bounded within the context of a dynamic task, the IBLT is a general theory of decision making applicable to other dynamic environments.

There has been significant interest in indirect measures of attitudes like the lmplicit Association Test (IAT), presumably because of the possibility of uncovering implicit prejudices. The authors derived a set of qualitative predictions for people's performance in the IAT on the basis of random walk models. These were supported in 3 experiments comparing clearly positive or negative categories to nonwords. They also provided evidence that participants shift their response criterion when doing the IAT. Because of these criterion shifts, a response panem in the IAT can have multiple causes. Thus, it is not possible to infer a single cause (such as prejudice) from IAT results. A surprising additional result was that nonwords were treated a. though they were evaluated more negatively than obviously negative items like insects, suggesting that low familiarity items may generate the pattern of data previously interpreted as evidence for implicit prejudice. What do you think of flowers? Would you evaluate them pos-itively? If so, what do you think of Larnists? Do you think a Larnist is more negative or more positive than a flower? As you may have realized, a Larnist is not an English word; we made it up. Presumably, you do not have a prestored opinion of Larnists, and

this article should be addressed to R. Goldstone, Psychology Department, Indiana University, Bloomington, IN 47405 (e-mail: rgoldsto@ indiana.edu). Further information can be found at http://cognitrn.psych. indiana.edu/ Similarity in context ROBERT L. GOLDSTONE DOUGLAS L. MEDIN Northwestern University, Evanston, Illinois and JAMIN HALBERSTADT Similarity comparisons are highly sensitive to judgment context. Three experiments explore context effects that occur within a single comparison rather than across several trials. Experiment 1 shows reliable intransitivities in which a target is judged to be more similar to stimulus A than to stimulus B, more similar to B than to stimulus C, and more similar to C than to A. Experiment 2 explores the locus of Tversky's (1977) diagnosticity effect in which the relative similarity of two alternatives to a target is influenced by a third alternative. Experiment 3 demonstrates a new violation of choice independence which is explained by object dimensions' becoming foregrounded or backgrounded, depending upon the set of displayed objects. The observed violations of common assumptions to many models of similarity and choice can be accommodated in terms of a dynamic property-weighting process based on the variability and diagnosticity of dimensions

Advocates of dynamic systems have suggested that higher mental processes are based on continuous representations. In order to evaluate this claim, we first define the concept of representation, and rigorously distinguish between discrete representations and continuous representations. We also explore two important bases of representational content. Then, we present seven arguments that discrete representations are necessary for any system that must discriminate between two or more states. It follows that higher mental processes require discrete representations. We also argue that discrete representations are more influenced by conceptual role than continuous representations. We end by

This paper illustrates how mechanisms initially designed for explaining analogy-making can also model judment and choice and account for contextual effects on these processes. The JUDGEMAP model is presented as well as three simulations that replicate some well known contextual effects in judgment and choice. It is demonstrated how the same basic mechanisms, designed for analogy-making can be responsible for seemingly unrelated phenomena, like the frequency effect in judgment and the concave form of the utility function; the preference for the middle ratings in judgment, the nonlinear form of subjective probability; and the effect of preference reversal.

ssing. We suggest that some types of similarity are determined automatically. When the cognitive system recognizes similarities, they influence cognitive processing, even when the person does not intend for their processing to be affected by similarities. In order to support this claim, we first outline three different approaches to similarity. Then, we examine how similarity can influence both low-level processes like attention and memory retrieval and higher cognitive processes like analogical reasoning and decision making. Next, we explore a number of examples in which cognitive processing is influenced by the presence of similarities in a stimulus set. Finally, we broaden the discussion to include similarities in more deliberate cognitive processes. Three Approaches to Similarity Representation and Similarity When a person makes a similarity comparison, the result is typically both a judgment of similarity and also some awareness of the commonalities and differences of the pair com

y be factored into the decision more heavily than is price. The execu- tive may choose to ride dow-ntown by taxi and then implement this decision by standing on line and taking a taxi to the hotel. To bring these sorts of decision situations into the laboratory, researchers commonly focused on the goal of obtaining money, which they assume is shared across people. In the prototypical task, subjects are given choice options that differ in probability and amount. The use of gambles enabled researchers to explore decision making under risk. Often, a number of different choices are made in a single experimental session, and the pattern of choices across sets is analyzed. For ample, people might be asked whether they prefer a 45% chance to win $200 or a 50% chance to win $150. Later in the same ses sion, they might be asked whether they prefer a 90% chance to win $200 or a 100% chance to win $150. At issue in studies like these is the consistency of people's choices. The anal- yses would in

Analogy and similarity are often assumed to be distinct psychological processes. In contrast to this position, the authors suggest that both similarity and analogy involve a process of structural alignment and mapping, that is, that similarity is like analogy. In this article, the authors first describe the structure-mapping process as it has been worked out for analogy. Then, this view is extended to similarity, where it is used to generate new predictions. Finally, the authors explore broader implications of structural alignment for psychological processing. Analogy and similarity are central in cognitive processing. They are often viewed as quite separate: Analogy is a clever, sophisticated process used in creative discovery, whereas similarity is a brute perceptual process that we share with the entire animal kingdom. This view of similarity has important implications for the way we model human thinking, because similarity is demonstrably important across many areas of cognition. We store experiences in categories largely on the basis of their similarity to a category representation or to stored exemplars (Smith & Medin, 1981). In transfer, new problems are solved using procedures taken

Aimee Drolet, Ellie Fang, Art Markman, Atanu Sinha, the helpful editor, and reviewers; and technical assistance from Carolyn Cohen, Jeff Robinson, Laura Brown, and Noe lle Triaureau. They also thank Bill Yost for recruiting participants from his class. The order of authorship is random. Address correspondence and reprint requests to Shi Zhang, 110 Westwood Plaza B412, UCLA--Anderson School, Los Angeles, CA 90095. Fax: (310) 206-7422. E-mail: shi.zhang@ anderson.ucla.edu. 192 0749-5978/99 $30.00 Copyright # 1999 by Academic Press All rights of reproduction in any form reserved. Making an option unavailable in this case would have a bigger impact than in a situation in which all options have nonalignable differences. Nonalignable differences are difficult to process and are less likely to make people aware that there is very much information about the options for decision making. This explanation and the interaction effect between option limitation and feature alignability